S  B 
955 
S67 
Entomol. 


v/-fy  /MMtia,  tfnrfcwuww  ww—j^ 


GAS    TREATMENT    FOR    SCALE 

INSECTS. 


TREATING  OF  THE  OPERATIONS  OF  THE  HORTICULTURAL  BOARD'S  FUMI- 
GATING OUTFIT,  THE  APPLICABILITY  OF  THE  FUMIGATION  PROCESS  IN 
CAPE  COLONY,  AND  EMBODYING  A  FULL  DESCRIPTION  OF  THE  EQUIP- 
MENT NECESSARY  FOR  FUMIGATION  WITH  HYDROCYANIC  ACID  GAS. 


Report  to  the    Horticultural    Board    by  the 
Government    Entomologist. 


JUNE,     1897. 


PRINTED  FOR  THE  BOARD   OF  HORTICULTURE 

BY 

TOWNSHEND"  TAYLOR  &  SNASHALL,  CAPE  TOWN. 


HON.  JOHN  X.  MERRIMAN, 

Chairman  of  Horticultural  Board. 

SIR, 

In  compliance  with  the  request  of  the  Horticultural  Board,  I 
herewith  submit  a  report  dealing  with  the  operations  of  the  Board's 
fumigation  outfit,  and  giving  detailed  information  in  regard  to  this 
most  effectual  remedy  for  the  Red  Scale  and  other  scale  insects 
affecting  citrus  trees. 

Respectfully  submitted, 

CHAS.  P.  LOUNSBURY, 

Government  Entomologist. 

Cape  Town, 

June,  1897. 


923 


CONTENTS. 


PAGE. 

Introductory               ...               ...  ....  ...      7 

Work  of  Horticultural  Board— 

NEED  OP  REMEDY  FOE  BED  SCALE  ...  ...      8 

RESOLUTION  OP  THE  BOARD       ...  ...  ...       8 

PREVIOUS  USE  OP  FUMIGATION  IN  CAPE  COLONY  ...       9 

PREPARATIONS  POR  THE  WORK  ...  ...  ...       9 

REVIEW  OF  OPERATIONS             ...  ...  ...  10 

CHARGES  POR  TREATMENT          ...  ...  ...  11 

OBJECT  OP  THIS  REPORT             ...  ...  ...  12 

ACKNOWLEDGMENTS                     ...  ...  ...  12 

The  Outfit— 

THE  TENTS              ...                  ...  ...  ...  13 

THE  SHEETS            ...                 ...  ...  ...  14 

OILING  OF  THE  CLOTH               ...  ...  ...  14 

UPRIGHTS  FOR  RAISING  THE  SHEETS  ...  ...  16 

OTHER  NECESSARIES                    ...  ...  ...  16 

Details  of  Treatment— 

GENERATION  OP  THE  G-AS           ...  ...  ...  17 

TIME  NECESSARY  FOR  THE  TREATMENT  ...  ...  17- 

ABSENCE  OF  SUN-LIGHT  NECESSARY  ...  ...  17 

SEASON  FOR  FUMIGATING            ...  ...  ...  18 

INJURIES  TO  THE  TREE              ...  ...  ...  18 

EFFICACY  OF  THE  GAS                ...  ...  ...  19 

QUANTITIES  OP  CHEMICALS         ...  ...  ...  20 

Cost  of  the  Equipment  and  Chemicals— 

EQUIPMENT               ...                 ...  ...  ...  23 

CHEMICALS               ...                 ...  ...  ...  24 

EXPENSE  COMPARED  TO  SPRAYING  ...  ...  24 

Nature  of  Hydrocyanic  Acid    ...  ...  ...  25 

General  Applicability  of  Fumigation  in  the  Colony ...  27 

Points  to  Remember  29 


GAS    TREATMENT    FOR    SCALE 
INSECTS. 


INTRODUCTORY. 


To  the  researches  of  American  investigators  and  the  experiences 
of  her  fruit  growers  is  due  the  credit  for  great  improvements  in 
insecticidal  washes  now  used  in  many  different  parts  of  the  world  ; 
and  to  the  same  source  we  owe  the  introduction  of  hydrocyanic  acid 
gas  for  the  destruction  of  scale  insects  in  the  orchard.  The  exped- 
iency of  a  gas  as  an  insecticide  for  scale  nsects  on  citrus  and  other 
evergreen  trees  arises  from  the  practical  impossibility  of  reaching 
all  the  insects  with  a  liquid  on  any  but  small  trees  ;  invariably,  some 
escape  destruction  011  large  trees  and  these  become  the  nuclei  of 
new  colonies  of  the  insects,  which  soon  become  as  great  a  pest  as 
before. 

The  destruction  of  insects  by  fumigation  with  poisonous  gases  or 
vapours  has  long  been  carried  on  in  greenhouses ;  but  that  the  pro- 
cess could  be  economically  practised  in  orchards  remained  to  be 
demonstrated  in  California  little  more  than  a  decade  ago.  In  the 
first  report  of  the  Board  of  State  Horticultural  Commissioners  of 
California,  published  in  1882,  unsuccessful  experiments  with  steam 
to  destroy  scale  insects  on  tent-covered  trees  without  injury  to  the 
foliage  are  recorded  by  Commissioner  S.  F.  Chapin.  A  few  years 
later,  Alexander  Craw,  the  present  entomologist  of  the  California 
State  Board  of  Horticulture,  and  Mr.  J.  W.  Wolfskill  carried  on 
many  experiments  with  a  number  of  different  gases.  The  work  of 
these  gentlemen  impressed  D.  W.  Coquillett,  then  a  special  agent  of 
the  Division  of  Entomology  of  the  United  States  Department  of 
Agriculture,  and  the  three  united  their  efforts.  Mr.  Coquillett  soon 
discovered  the  value  of  hydrocyanic  acid  gas  for  the  purpose.  This 
happened  in  the  latter  part  of  the  year  1886.  In  a  short  titoe, 
fruit  growers  began  to  avail  themselves  of  the  discovery ;  at  first 
slowly,  and  then  more  rapidly  as  improved  methods  of  applying  the 
gas  were  devised  until  the  "  fumigation  process  "  superseded  to  a 
very  great  extent  the  use  of  washes  on  citrus  trees  in  California. 


WORK    OF    HORTICULTURAL    BOARD. 


Need  of  Remedy  for  Red  Scale. —Our  colonial  citrus  orchards 
have  long  been  afflicted  with  the  Red  Scale.  By  applications  of 
washes,  frequently  and  thoroughly,  some  of  the  most  enlightened 
growers  have  managed  to  clean  small  trees  and  to  keep  the  scales 
well  in  check  on  large  ones ;  but  the  expense  and  trouble  for  these 
results  have  been  too  great  to  induce  the  mass  of  growers  to  spray. 


BED  SCALE,  Aspidiotus  auranlii  Mask.  1,  infested  leaves ;  la,  male ;  16,  cmale 
scale  ;  Ic,  male  scale  ;  1  is  natural  size  and  the  others  are  much  enlarged.  (From 
U.S.A.  Dept.  Agr.) 

The  Red  Scale  is  by  far  the  most  injurious  scale  insect  affecting  citrus  trees  in  this 
colony  and  in  most  other  countries. 

Orchards  have  fallen  into  neglect,  and  consequently,  with  the 
increasing  demand,  oranges  and  lemons  have  become  scarce  and 
high-priced. 

Resolution  of  the  Board. — The  Horticultural  Board  realized  the 
necessities  of  the  case  and  determined  to  do  its  utmost  to  popularize 
remedies.  A  resolution  was  passed  during  March  of  last  year  to 
utilize  certain  funds  placed  at  its  disposal  by  Parliament  in  provid- 
ing a  demonstration  on  a  large  scale  which  would  prove  the  value 


9 

and  economy  of  remedial  measures  against  this  insect.  Fumigation 
was  finally  chosea  as  the  chief  means,  for  while  perfectly  aware  that 
this  treatment  could  not  be  universally  adopted  by  private  parties 
owing  to  the  initial  expenses,  it  was  also  recognised  that  it  had 
proven  best  iu  California,  and  that  if  it  was  popularized  in  the 
colony,  co-operation  among  growers  or  private  enterprise  could  bring 
it  within  the  means  of  a  large  proportion  of  the  growers. 

Previous  Use  of  Fumigation  in  Cape  Colony.— The  first 

use  of  hydrocyanic  acid  gas  to  substitute  spraying  in  Cape  Colony 
was,  it  is  believed,  by  Mr.  P.  J.  Cillie,  C'son,  of  Wellington,  who  as  a 
Government  delegate  had  been  to  California  during  1893  to  acquire 
general  horticultural  information  for  the  benefit  of  colonial  fruit 
growers.  Mr.  Cillie  had  a  few  tents  prepared  shortly  after  his 
return  and  fully  corroborated  the  Californian  experience  that 
fumigation  with  the  gas  was  far  more  efficacious  than  spraying  with 
the  very  best  of  washes  by  cleaning  a  number  of  citrus  trees  in 
different  parts  of  Wellington.  At  about  the  same  time  that  Mr. 
Cillie  was  working  with  the  process,  another  enterprising  fruit 
grower,  Mr.  Henry  Meyers,  of  Nawlands  in  the  Cape  Division, 
undertook  to  fumigate  his  orchard.  But  altogether  these  attempts  to 
make  fumigation  a  factor  in  the  colonial  fruit  industry  threatened  to 
come  to  naught  through  the  many  obstacles  which  the  introduction  of 
new  means  and  appliances  meets  in  colonies;  the  principal  one  of  which 
is,  perhaps,  the  great  difficulty  of  obtaining  small  quantities  of  the 
necessary  materials  at  prices  which  leave  any  margin  of  profit 
before  a  steady  demand,  with  consequent  lowering  of  the  cost  of 
importation,  has  been  created. 

Preparations  for  the  Work-— The  real  need,  then,   was  to 

encourage  and  populari/e  this  remedial  measure,  thus  creating  a 
demand  for  the  treatment  which  would  bring  the  expense  within 
the  limits  of  economy;  or,  what  really  amounts  to  the  same  thing, 
to  prove  by  an  object  lesson  that  with  proper  management  the 
expense  is  not  prohibitive.  In  July,  the  Government  Entomologist, 
whose  services  are  available  to  the  Board  through  the  courtesy  of 
the  Department  of  Agriculture,  was  instructed  to  have  an  outfit 
prepared  and  to  proceed  to  fumigate  the  citrus  orchards  in  Welling- 
ton. Cyanide  for  the  work  was  at  once  ordered  from  the  German 
manufacturers,  who  furnish  much  of  that  used  in  California ;  and 
the  actual  work  of  fumigation  was  in  progress  by  the  1st  of 
September. 

The  Wellington  members  of  the  Board,  Mr.  P.  J.  Cillie  and  Mr.  J . 
F.  Pentz,  worked  in  conjunction  with  the  Entomologist  in  the  initial 
arrangements,  and  the  latter  member  rendered  still  more  valuable 
service  by  keeping  a  general  oversight  of  the  work  while  the  outfit 
remained  in  Wellington.  The  direct  superintendence  of  the  work 
was  entrusted  to  Mr.  P.  J.  Pentz,  also  of  Wellington.  Three 
coloured  labourers  completed  the  staff.  The  Entomologist  planned  the 


10 

work>  purchased  the  supplies,  and,  in  short,  supervised  the  whole 
work,  visiting  the  scene  of  operations  on  an  average  of  once  a  foit- 
night. 

Review  of  Operations-— The  outfit  was  kept  in  Wellington 
during  the  months  of  September,  October  and  November,  during 
which  time  about  2,000  trees  were  fumigated  on  23  farms.  The  gre^t 
majority  of  the  trees  were  in  wretched  condition ;  they  were  of  all 
sizes,  two  of  the  same  height  standing  side  by  side  being  the  excep- 
tion, not  the  rule.  Arrangement  in  orchard  form  was  generally 
absent,  and  on  most  of  the  farms  vines  were  grown  among  the  trees. 
These  factors  greatly  impeded  the  work,  and  in  connection  with  the 
numerous  delays  caused  by  unfavourable  weather  (rain,  wind  and 
heavy  dews)  explain  the  slowness  of  the  work. 

The  neglected  state  of  the  Wellington  trees  must  not  be  taken  to 
reflect  upon  Wellington  farming  ;  it  is  simply  the  natural  sequence 
of  the  trees  ceasing  to  be  profitable,  which  in  turn  is  brought  about 
through  the  ravages  of  scale  insects.  Most  of  the  trees  had  once- 
stood  in  rows  and  in  a  way  still  stand  in  them,  but  great  gaps  and 
uneven  growth  disguise  the  arrangement. 

In  early  December,  the  outfit  was  taken  to  the  Paarl  to  enable 
the  fruit  growers  there  to  become  acquainted  with  the  process. 
About  400  trees  were  treated  on  three  farms  in  the  Groot  Drakeii- 
stein  ward.  For  the  benefit  of  the  Stellenbosch  parties  who  were 
interested,  the  outfit  was  then  taken  to  Ban  Hoek  in  that  division. 
Here  500  trees  were  fumigated  on  one  farm.  It  then  became  neces- 
sary to  postpone  further  work  until  the  arrival  of  supplies  of 
cyanide.  Work  was  resumed  at  the  t'me  of  the  Western  Province 
Agricultural  Show  at  Kosebank  (February  25th  and  26th),  when 
demonstrations  were  held  in  a  garden  close  by  the  Show  Grounds 
for  the  benefit  of  those  attending  the  show.  The  Constantia 
Fruit  Growers  were  then  invited  to  witness  the  operations  in  orchards 
at  JSTewlands  where  about  200  trees  were  treated. 

No  single  estate  in  the  colony,  probably,  is  more  visited  by  farmers 
than  Lourensford  at  Somerset  West.  Here  were  large  orchards 
where  the  outfit  could  be  worked  to  good  advantage  and  where 
numerous  visitors  would  see  the  results  of  the  work.  The  outfit  was 
taken  to  this  place  during  the  first  week  of  March,  and  despite  of 
almost  incessant  high  winds  and  several  rain  storms  1,600  trees  were 
fumigated  during  the  following  month.  At  the  urgent  request  of 
the  owners,  the  outfit  was  then  taken  to  farms  in  Ban  Hoek,  and 
1,015  trees  on  four  farms  were  treated  at  figures  estimated  to  cover 
the  cost  of  the  work.  Worcester  was  then  visited,  and  the  fruit 
growers  of  that  vicinity  invited  to  witness  the  treatment  of  trees  at 
Glen  Heatlie.  Goudini  was  next  visited,  and  about  200  trees  fumi- 
gated on  a  farm  belonging  to  the  Field-cornet.  Lastly,  225  trees  were 
treated  on  one  farm  at  Eiebeck  West  in  the  Malmesbury  Division. 

In  all  above  6,000  trees  have  been  fumigated.  These  are  distributed 
among  five  divisions  and  one  or  another  is  within  easy  access  of 


11 

most  Western  Province  orange  growers.  These  people  therefore 
have  only  themselves  to  blame  if  they  do  not  learn  by  actual 
observation  the  magnificent  results  achieved  by  the  fumigation 
process. 

Charges  for  Treatment.— At  Wellington,,  a  nominal  charge  of 
3d.  for  each  tree  fumigated  was  made ;  arid,  as  elsewhere,  the 
beneficiaries  were  required  to  attend  to  the  conveyance  of  the 
outfit  from  one  farm  to  another.  It  was  deemed  advisable  to 


BROWN  OR  SOFT  SCALE,  Lecanium  hesperidum  Linn.  An  infested  twig. 
(From  U.S.A.  Dept.  Agr.) 

The  Brown  Scale  is  found  in  most  parts  of  the  colony  and  in  some  districts  is  very 
injurious  to  citrus  trees. 

make  only  this  small  charge  at  first  in  order  to  be  certain  of 
securing  work,  and  it  was  presumed  that  as  the  charge  was 
merely  nominal,  the  profiting  farmers  would  facilitate  the  work  by 
being  accommodating  in  the  matter  of  conveyance.  But  this 
presumption  proved  quite  erroneous.  The  treatment  which  the 
agents  of  the  Board  received  at  the  hands  of  many  (not  all)  of  the 
Wellington  farmers  whose  trees  were  fumigated  was  anything  but 
liberal,  and  seemed  prompted  by  the  contemptible  spirit  that  tjie 
Government  is  a  lawful  prey  to  be  bled  whenever  opportunity  arises. 


12 

The  charges  for  the  work  since  leaving  Wellington  have  been 
made  with  a  view  to  cover  the  actual  costs,  disregarding  wear  and 
tear  to  the  outfit  and  the  time  lost  in  moving  about.  These  chargf  s 
in  general  have  been  6d.  for  trees  under  eight  feet  in  height,  and  Is. 
for  ti:ose  above.  The  increased  charges  were  necessary  to  keep  up 
the  work,  as  the  funds  were  nearing  exhaustion,  but  they  appear  to 
have  proved  an  advantage  in  other  respects.  The  work  has  been 
more  appreciated,  and  every  assistance  given  to  facilitate  it,  no 
trouble  at  all  being  made  about  the  conveyance  of  the  equipment, 
however  great  the  distance. 

The  movements  of  the  outfit  have  been  advertised  from  time  to 
time  in  the  newspapers,  and  the  public  have  been  invited  to  be 
present  at  stated  times  in  the  different  towns  when  full  explanations 
of  the  process  have  been  given  by  the  foreman. 

Object  of  this  Report. — This  report  is  written  at  the  request 
of  the  Board  to  supplement  the  field  work  by  giving  full  particulars 
of  the  process  and  of  the  equipment ;  and  to  point  the  way  for 
others  to  take  up  the  work  where  the  Board  leaves  it. 

The  object-lesson  of  the  efficacy  of  fumigation  is  now  before  the 
public.  An  inspection  of  the  trees  shows  them  to  have  improved 
wonderfully  since  the  treatment,  and  farmers  are  enthusiastic  over 
the  results.  The  Board's  field  work  is  finished.  There  are  many 
disadvantages  in  carrying  on  a  work  of  this  kind  through  the 
Grovernment  or  body  like  tne  Horticultural  Board,  and  now  that 
several  thousand  trees  have  been  successfully  treated,  there  is  no 
longer  any  reason  for  the  Board  to  continue  the  work.  ^N"ot  every 
day  is  suitable  for  fumigating  trees,  but  as  the  foreman  and  his  men 
were  working  away  from  home,  they  had  to  be  paid  for  days  when 
no  work  was  done  equally  with  those  when  they  were  employed. 
This  loss  of  time  greatly  augmented  the  expense,  but  is  a  factor 
which  would  be  largely  obviated  if  the  work  was  done  by  the 
farmers  themselves,  or  by  a  local  party  with  other  employment  for 
himself  and  men  when  fumigation  could  not  be  carried  on  to 
advantage. 

Acknowledgments. — As  stated  in  the  introductory  paragraph, 
we  are  following  Calif ornian  precedents.  The  outfit  employed  by 
the  Board  was  modelled  after  those  employed  by  the  Los  Angeles 
County  Horticultural  Commission  as  described  in  California!! 
publications;  other  details  were  furnished  by  Horticultural  Corn- 
mi- siojier  John  Scott,  of  the  same  couuty,  in  correspondence  with 
the  Entomologist.  The  full-page  illustrations  were  purchased  from 
the  Calif  ornian  State  Board  of  Horticulture;  they  were  engraved 
from  photographs  of  the  Los  Angeles  County  Horticultural  Commis- 
sion's outfit.  The  illustrations  of  the  red  and  other  scale  insects 
were  obtained  from  the  United  States  Department  of  Agriculture, 
through  the  kindness  of  Dr.  L.  0.  Howard,  the  Entomologist  of  the 
Department. 


THE    OUTFIT. 


The  fumigation  outfit  of  the  Horticultural  Board  consists  of  tents, 
poles  and  other  paraphernalia,  as  hereunder  described. 

Th.6  Tents. — These  are  22  in  number,  and  are  used  for  covering1 
trees  under  12  feet  in  height.  Th>y  are  made  dome-shaped,  the 
upper  portion  being  curved  like  the  surface  of  a  hemisphere  and  the 
lower  portion  being  of  uniform  character.  What  is  known  as 
"  eight-ounce  Burlington  duck  "  was  most  largely  used  in  making  the 
tents  ;  but  two  other  makes  of  American  ducks,  "  Greenwoods  "  and 
"  Savannah,"  were  also  employed.  These  cloths  come  in  various 
widths,  but  it  was  found  most  economical  to  use  the  narrowest  width, 
that  of  27  inches. 

When  this  width  of  cloth  is  used,  the  proper  curve  of  the  tent 
may  ,be  obtained  by  cutting  the  cloth  on  the  line  of  an  arc  drawn 


The]space  within  the  outside  lines  represents  the  end  of  breadth  before  cutting 
that  within  the  curved  lines,  the  same  after  cutting,     m  marks  the  middle  of  the 
end.Jc,  the  point  in  the  side,  I,  the  straight  connecting  line  and  h,  the  3£  inch  line. 


from  the  middle  of  the  end  of  the  breadth  to  the  point  on  either  sidt 
distant  one-fourth  of  the  circumference  of  the  completed  tent,  and 
passing  through  a  third  point  3J  inches  out  from  the  straight  line 
connecting  the  first  points.  The  accompanying  sketch  will  serve  to 
make  the  meaning  clearer.  Board  models  of  the  required  length, 
3J  inches  at  the  middle  and  curving  gradually  to  the  ends,  were 
found  to  be  a  great  convenience  in  delineating  the  curves. 

The  crowns  of  the  tent  are  reinforced  both  inside  and  out  with 
extra  pieces  of  cloth,  and  rope  loops  are  attached  to  the  crowns  both 
inside  and  out  for  convenience  in  handling  the  tents. 

The  tents  in  use  are  of  four  sizes  : — I.,  eight  made  of  six  breadths, 
2J  y^rds  in  length  ;  II.,  eight  of  9  breadths,  3  yards  in  length;  III., 
three  of  11  breadths,  4  yards  in  length;  and  IV.,  three  of  13 


14 

breadths,    5J   yards   in   length.     The  breadths  in  all  cases   are  27 
inches  in  width. 

A  circle  of  gas-pipe  is  used  to  keep  the  mouth  of  each  tent 
expanded.  The  circle  is  made  in  halves ;  the  ends  are  joined  by 
short  pieces  of  larger  pipe  into  which  they  slip  and  are  held  in  place 
by  loosely-fitting  bolts  passing  through  holes  drilled  through  both 
the  end  of  the  circle  and  the  short  connecting  piece.  Before  the 
ends  are  connected  the  halves  are  attached  to  the  tent  by  passing 
them  through  iron  rings  sewn  to  the  tent  about  one  foot  from  the 
bottom.  These  rings  fit  loosely.  On  all  but  the  smallest  tents,  one 
is  attached  at  each  seam;  the  smallest  tents  have  three  to  each 
two  breadths.  It  would  have  been  better  to  have  used  three  to  each 
two  breadths  on  all  the  tents ;  the  cloth  should  be  reinforced  where 
they  are  attached. 

A  stout  pole  ending  in  a  U-shaped  iron  rest  is  used  to  support  the 
crowns  of  the  larger  tents  in  placing  them  over  and  in  removing 
them  from  the  trees;  the  rest  is  hooked  in  the  rope  loops. 

The  Sheets. — The  sheets  are  made  in  the  form  of  a  regular 
octagon.  They  are  six  in  number,  and  vary  from  32  to  48  feet 
across.  Widths  of  cloth  from  27  inches  to  10  feet  were  used  in  the 
construction  of  different  sheets,  but  it  was  found  most  economical  to 
use  the  narrowest  width,  the  additional  expense  for  sewing  being  less 
than  the  relatively  greater  value  of  the  cloth.  Ten-ounce  duck  was 
used  for  the  middle  breadths  of  equal  length,  and  eight-ounce  duck 
for  the  breadths  outside  of  these.  It  is  not  believed  that  the  heavier 
cloth  added  sufficient  to  the  strength  to  make  its  use  desirable,  and 
if  other  sheets  were  now  to  be  made,  eight-ounce  duck  throughout 
would  be  employed. 

In  cutting  the  cloth  to  secure  the  octagonal  shape,  little  trouble 
will  be  experienced  if  it  is  remembered  that  one  side  of  a  regular 
octagon  is  equal  to  about  five-twelfths  of  the  total  length,  and  that 
each  breadth  will  be  its  own  width  shorter  outside  than  the  breadth 
next  to  it  toward  the  middle.  For  instance,  in  an  octagonal  sheet  54 
feet  across  made  from  cloth  27  inches  wide,  the  ten  middle  breadths 
are  the  full  length  of  54  feet,  the  next  breadth  on  each  side  is  54 
feet  on  the  inside  and  twice  its  own  width  or  4|  feet  less  than  54 
feet  on  the  outside.  By  cutting  the  breadth  for  the  two  sides 
alternately  there  will  be  only  one  mitre  of  cloth  wasted. 

Both  sheets  and  tents  were  sewed  by  machine  with  heavy  linen 
thread  (principally  Barber's  No.  35) .  The  seams  in  the  tents  were 
run  down  once  only,  while  those  in  the  sheets  were  turned  over  and 
sewed  a  second  time,  as  the  strain  on  the  cloth  is  much  greater  in  the 
sheets  than  in  the  tents. 

Oiling  of  the  Cloth. — To  make  the  tents  and  sheets  impervious 
to  the  gas,  the  cloth  after  being  made  up  was  brushed  with  a 
mixture  of  four  parts  of  boiled  linseed  oil  to  one  part  of  turpentine. 


15 

The  cloth  was  first  well  wetted  with  water,  and  then  the  mixture  was 
spread  lightly  over  the  surface  with  a  flat  brush.  A  thin  coating 
was  found  to  be  sufficient.  The  turpentine  causes  the  oil  to  dry 
more  rapidly  than  it  would  otherwise  do.  One  gallon  of  the  mixture 
was  used  to  cover  about  25  running  yards  of  the  cloth.  After  being 
oiled,  the  tents  were  hung  from  trees  and  the  sheets  spread  out  on  the 
ground  and  left  until  they  were  dry.  Failure  to  thoroughly  dry  the 
cloth  before  rolling  it  up  may  prove  its  destruction,  as  it  is  liable  to 
take  fire  by  spontaneous  combustion. 

In  California,  an  extract  of  the  juice  of  a  species  of  prickly  pear 
(Opuntia  engelmani),  to  which  is  added  a  little  sizing  and  yellow 


OLEANDER  SCALE,  Aspidiotus  nerii  Bouche.  1,  infested  Acacia  twig  :  la,  male  ; 
16,  male  scale  ;  Ic,  female  scale ;  I  is  natural  size  and  the  others  are  much  enlarged. 
(From  U.S.A.  Dept.  Agr.) 

The  Oleander  Scale  is  common  in  the  colony  but  not  common  on  citrus  trees; 
it  is,  however,  very  injurious  to  citrus  trees  in  an  orchard  at  Hex  River  and  is  very 
common  on  European  fruit. 

ochre,  is  used  to  substitute  oil  for  coating  the  cloth.  This  prepara- 
tion has  the  advantage  of  leaving  the  cloth  much  lighter  and  more 
pliable  than  oil,  besides  being  much  less  expensive.  Thus  treated, 
sheets  up  to  60  feet  across  are  manageable,  while  oiled  sheets  of  this 
size  would  be  too  great  a  strain  on  the  poles  commonly  used.  Many 
attempts  were  made  to  utilize  the  extract  of  our  prickly  pear 
(Opuntia  tuna)  for  the  purpose,  but  all  ended  in  total  failure  ;  the 
cloth  was  as  pervious  after  the  treatment  as  before.  Another 
Calif  ornian  practice  is  to  sew  a  "  skirt  "of  lighter  material  than 


1(5 

duck,  usually  "drill/'  around  the  sheets,  thus  securing  greater 
dimensions  with  little  extra  weight. 

Uprights  for  Raising  the  Sheets.— Those  take  the  place  of 

derricks  and  other  cumbersome  appliances  used  by  the  first 
fumigators.  Two  are  used,  one  at  each  side  of  the  tree.  Those 
employed  in  the  Board's  outfit  are  made  of  straight-grained,  knotless 
pitch  pine  deal.  This  wood  was  the  most  suitable  of  any  obtainable 
in  Cape  Town.  The  principal  piece  of  each  is  a  pole,  2x4  inches  in 
section  and  25  feot  in  length.  Cross  pieces,  1  x  3  in  section  and  6 
feet  long  are  bolted  to  each  side  at  the  bottom ;  and  braces  of  2  x  4 
inches,  5  feet  long,  also  bolted  in  place,  extend  from  between  the 
ends  of  the  cross  pieces  to  the  upright  piece.  A  guy  rope,  £  inch  in 
diameter  and  35  feet  long,  is  attached  to  the  top  of  each  upright.  A 
rope  of  ^  inch  diameter  and  75  feet  long  answers  for  tackle ;  this 
is  passed  through  a  fixed  pulley  at  the  top  of  the  pole  and  then 
through  a  movable  pulley,  and  thence  back  to  the  top  of  the  pole. 
The  movable  pulleys  are  in  view  in  the  illustration.  The  sheet  is 
gathered  four  or  five  feet  from  the  margin  and  a  hitch  made  about 
the  gather  with  a  short  piece  of  rope,  which,  when  all  is  ready  tor 
raising  the  sheet,  is  attached  to  the  movable  pulley.  This  arrange- 
ment is  superior  to  hitching  the  pulley-hook  to  a  ring  or  loop  sewed 
to  the  sheet,  as  the  resulting  strain  when  the  sheet  is  raised  is  far  less 
on  the  cloth. 

To  use  the  uprights,  one  is  laid  at  either  side  and  the  sheet  dropped 
behind  the  tree;  the  hitch  is  then  made  and  the  tackle  attached. 
The  four  men  then  raise  the  poles,  and  when  these  are  vertical,  two  of 
the  operators  steady  them  by  means  of  the  guy  ropes,  while  the 
other  two  raise  the  sheet  by  pulling  on  the  tackle.  When  raised 
sufficiently  (see  the  illustration),  the  poles  are  allowed  to  drop  slowly 
forward,  thus  bringing  the  sheet  over  the  tree  and  in  position. 

Other  Necessaries. — The  generating  vessels  are  of  lead,  this 
metal  being  chosen  because  of  its  durability  and  resistance  to  the 
chemicals  employed  in  the  generation  of  the  gas.  The  vessels  are 
bowl-shaped  and  vary  from  4  inches  in  diameter  by  2  inches  in  depth 
to  8  inches  in  diameter  by  6  inches  in  depth.  Small,  heavy,  porcelain 
dishes  are  used  when  the  quantities  of  the  chemicals  are  very  slight. 
Porcelain  or  enamel- ware  dishes  will  answer  as  substitutes  for  lead 
for  all  sizes  of  trees  but  are  less  economical  when  much  work  is  to  be 
done  because  of  their  less  durability. 

Carefully  balanced  scales  are  used  for  the  weighing  of  the  cyanide ; 
the  brass  pans  of  these  are  protected  by  enamel-ware  plates. 
Measure  glasses  graded  for  fluid  ounces  are  used  for  measuring  the 
water  and  acid  required  to  liberate  the  gas. 

A  tent  for  sheltering  the  supplies  of  chemicals,  a  chest  in  which 
sundries  are  locked,  half  a  dozen  lanterns,  lantern  rests,  spades, 
buckets,  heavy  bottles  for  temporarily  holding  small  quantities  of  the 
acid,  and  air-tight  tins  for  similar  use  with  the  cyanide,  complete  the 
equipment. 


Sheet  for  Covering  Citrus  Trees  Preparatory  to  Fumigating, 


DETAILS    OF    TREATMENT. 


Generation  of  the  Gas- — Hydrocyanic  acid  gas  is  generated  by 
the  action  of  sulphuric  acid  on  potassium  cyanide  in  the  presence  of 
water.  The  required  quantities  of  the  cyanide  and  water  are  first 
placed  in  the  generating  vessel,  the  cyanide  being  then  covered  with 
the  tent  or  sheet  and  the  vessel  slipped  under  almost  to  the  base  of 
the  tree ;  reaching  in,  the  operator  then  adds  the  acid,  pouring  it 
slowly  into  the  vessel  so  as  to  avoid  its  splashing  and  thus  burning 
his  hand  or  the  cloth.  He  immediately  withdraws  and  the  men 
shovel  a  little  soil  on  the  edges  of  the  cloth  all  around  to  more 
thoroughly  prevent  the  escape  of  the  gas. 

The  rapidity  of  the  evolution  of  the  gas  depends  largely  upon  the 
size  of  the  pieces  of  cyanide.  If  these  are  like  powder,  the  reaction 
is  violent  and  immediate;  but  if  in  lumps,  the  reaction  takes  place 
more  slowly  and  continues  for  a  minute  or  longer.  The  slow  reaction 
is  desired,  partly  because  less  injury  results  to  the  foliage  immediately 
above  the  vessel.  But  the  lumps  must  not  be  too  large,  for  then  the 
reaction  is  liable  to  be  imperfect  owing  to  a  black  coating  (carbon  ?) 
forming  over  the  lumps  and  preventing  further  decomposition  by  the 
acid.  The  water  should  not  be  added  too  soon  or  part  of  the  cyanide 
becomes  dissolved  and  gives  a  violent  reaction.  The  residue  which 
remains  in  the  dishes  is  buried ;  and  the  dishes  are  washed  in  clean 
water  before  being  again  used. 

The  weighing  of  a  large  number  of  doses  at  one  time  and  keeping 
them  in  envelopes  or  boxes  until  used  was  attempted  but  found  to  be 
disadvantageous  owing  to  the  affinity  of  the  cyanide  for  water. 

Time  Necessary  for  Treatment, — The  cover  is  left  over  the  tree 

for  thirty  minutes  in  the  case  of  small  trees  and  forty-five  in  the  case 
of  those  over  twelve  feet  in  height.  At  the  expiration  of  this  period 
the  generating  vessel. is  removed  and  the  residue  buried  in  the  soil; 
the  dish  is  then  washed  out  preparatory  to  treating  another  tree. 

A  number  of  trees  are  fumigated  together,  the  endeavour  being  to 
treat  as  many  at  a  time  as  can  be  covered  and  uncovered  during  the 
period  of  exposure.  In  this  way  the  men  are  kept  continuously  busy, 
the  time  for  the  removal  of  the  first  tent  arriving  by  the  time  that 
the  last  tree  is  covered.  The  largest  number  of  trees  fumigated 
during  one  night  has  been  190.  The  average  number  has  been  only 
a  small  fraction  of  this  number  owing  to  the  delays  caused  by  high 
winds  and  rains,  and  in  the  conveyance  of  the  outfit  from  farm  to 
farm  and  town  to  town.  On  several  occasions,  inclement  weather 
prohibited  the  work  four  nights  in  the  week,  and  at  one  time  there 
were  but  two  really  favourable  nights  for  a  period  of  three  weeks. 

Absence  of  Sunlight  Necessary. — The    originators    of    the 

fumigation  process  observed  that  the  gas  was  most  efficacious  and  that 


IS 

less  injury  resulted  to  the  foliage  when  the  operations  were  performed 
at  night  than  when  they  were  carried  on  in  sun-light.  It  is  said  that 
chemical  changes  are  produced  in  the  gas  by  the  action  of  sun-light 
and  that  the  resulting  gases  are  more  injurious  to  the  plant  life 
and  less  to  animal  than  hydrocyanic  acid  gas.  Whether  or  not  these 
theories  are  correct  is  of  small  practical  importance,  for  the  foliage  of 
a  tree  will  suffer  serious  injury  if  the  tree  is  left  covered  with  an  air- 
tight oiled  tent  for  half  an  hour  in  sun-light,  without  the  gas  being 
present.  Having  ascertained  this  fact,  by  experience,  the  foreman  in 
charge  of  the  Board's  outfit  refrained  from  covering  trees  until  the 
sun  had  sunk  from  sight  on  any  but  cool,  dull  days.  The  great  majority 
of  the  trees  treated  have  been  fumigated  after  sunset.  The  ideal 
night  for  fumigating  is  quiet,  cool,  and  moon-light,  and  without  dew. 

Season  for  Fumigating.— The  operations  may  be  successfully 
conducted  against  the  Red  and  Brown  Scales  at  any  season  of  the 
year.  The  chances  for  thoroughly  effectual  work  are  best,  perhaps, 
during  the  latter  part  of  February  and  March,  when  young  insects  are 
most  abundant.  The  operations  of  the  Board  began  late  in  August 
and  have  continued  through  to  June  without  intermission  save  for  the 
first  six  weeks  of  the  year,  when  work  was  suspended  owing  to  the 
non-arrival  of  supplies  of  cyanide,  and  during  this  period  the  treat- 
ment has  been  uniformly  successful. 

Injuries  to  the  Tree.-  -Injury  to  the  tips  of  new  growth  gener- 
ally results.  This  injury  is  in  no  wise  serious  and  is  quickly  out- 
grown. The  operators  consider  it  a  favourable  indication,  as  when 
such  injury  results  it  is  quite  certain  that  the  gas  has  been  present  in 
sufficient  strength  to  destroy  all  of  the  insects.  When  no  "  burn- 
ing "  results,  there  is  always  the  suspicion  that  not  enough  cyanide 
was  used. 

The  blossoms  appear  to  be  less  affected  than  the  foliage  and  very 
little  damage  is  caused  to  them.  The  fruit,  likewise,  is  not  sensitive 
but  a  little  generally  drops  after  a  few  days  ;  this  dropping  may  be 
due,  in  part  at  least,  to  mechanical  injury  in  raising  and  lowering  the 
cloth. 

If  a  heavy  overdose  is  administered,  all  of  the  foliage  and  fruit 
may  fall  and  the  young  wood  die  back.  Very  small  trees  are  most 
likely  to  receive  an  overdose ;  and  unless  trees  under  four  feet  in 
height  by  three  in  diameter  are  badly  infested  with  scale  insects,  it 
is  best  not  to  risk  injuring  them.  Any  excess  given  to  a  tree  of  even 
this  size  will  cause  as  much  damage  as  seven  times  the  same  excess 
given  to  a  tree  of  double  the  dimensions.  These  remarks  apply  only 
when  the  trees  are  treated  singly,  not  when  a  number  are  treated 
under  the  one  tent,  as  can  be  safely  done  in  nursery  rows.  If  many 
small  trees  are  to  be  treated,  a  frame  to  keep  the  tent  expanded  to 
encompass  a  space  for  which  a  dose  can  be  safely  administered,  had 
best  be  used. 


19 

Lemon  and  citron  trees  are  more  sensitive  than  orange  and  greater 
care  must  be  taken  not  to  overdose  them.  Decreasing  the  amount  of 
cyanide  by  ten  per  cent,  when  lemon  trees  are  treated  is  recommended 
in  California. 

Efficacy  Of  the  Gas  — Applied  sufficiently  strong  and  under  a 
tight  tent,  every  living  scale  insect  appears  to  be  destroyed.  These 
perfect  results  are  not  always  obtained  in  practice  despite  of  care  in 
keeping  the  outfit  in  good  order ;  but  living  scales  have  been  found 
on  few  of  the  trees  fumigated  a  few  weeks  after  the  treatment.  A 


BLACK  SCALE,  Lecanium olecc  Bern.  1,  an  infested  twig;  la,  an  enlarged  scale. 
<From  U.S.A.  Dept.  Agr.) 

The  Black  Scale  has  seldom  been  seen  on  citrus  trees  in  this  country  but  is  very 
injurious  to  these  trees  in  California. 

number  of  trees  suffering  from  Purple  Scale  have  been  fumigated, 
and  the  eggs  as  well  as  the  insects  themselves  have  succumbed.  This 
success  was  unlocked  for  and  may  not  always  follow ;  it  may  also  be 
that  some  of  the  eggs  escaped  although  those  under  several  hundred 
scales  examined  were  all  destroyed. 

Experiments  conducted  in  the  fumigation  chamber  owned  by  the 
Department  of  Agriculture  and  situated  near  the  gates  to  the  Cape 
Town  Docks  have  demonstrated  that  when  the  gas  is  used  somewhat 
stronger  than  is  the  practice  in  orchards,  every  scale  insect  and  scale 
insect  egg  is  destroyed.  The  Australian  Bug  was  among  the  insects 


20 


enclosed  in  the  chamber,  and  not  a  single  egg  hatched  among  tens  of 
thousands  exposed. 

Notwithstanding  the  efficacy  of  the  gas,  however,  it  is  quite  an 
impossible  task  to  exterminate  the  Eed  Scale  where  it  has  long  been 
established,  for  not  only  does  the  scale  infest  citrus  trees  but  other 
orchard  trees  and  many  garden  plants  and  even  some  ornamental 
trees  like  the  Seringa  (Melia  azedarach) ,  Keurboom,  Willow,  and 
Cypress.  It  usually  occurs  in  the  greatest  abundance  on  the  citrus 
trees  and  it  is  generally  from  them  that  the  other  plants  become 
infested;  but  when  the  citrus  trees  are  cleaned,  it  is  but  reasonable 
to  suppose  that  the  insect  will  in  time  find  its  way  to  them  from 
these  other  trees.  Rose  bushes  are  very  frequently  infested,  and  as 
these  plants  are  to  be  found  on  almost  every  farm,  the  infection  is 
very  likely  to  spread  from  them  to  the  citrus  trees.  It  may  be  one 
year  or  two  years  or  even  longer  before  the  citrus  trees  become 
noticeably  affected,  but  sooner  or  later,  the  insect  is  quite  sure  to  get 
to  them  and  to  again  require  attention. 

The  tents  and  sheets  should  be  examined  each  day,  when  all  rents- 
and  holes  should  be  covered  by  patches.  A  small  piece  of  cloth 
about  holes  caused  by  the  acid  should  be  cut  away  or  the  acid  will 
continue  to  destroy  the  fibre.  The  fumigation  of  trees  covered  by 
cloth  containing  holes  is  very  apt  to  be  a  complete  failure. 

Quantities  of  Chemicals. — The  following  table  gives  the 
quantities  of  the  chemicals  used  for  various  sizes  of  trees  by  the 
iumigators  for  the  Horticultural  Board. 


Height. 

Diameter. 

Water. 

Acid. 

Cyanide. 

Space  enclosed. 

Feet. 

Feet. 

Fluid  oz. 

Fluid  oz. 

Oz. 

Cubic  Feet. 

4 

3 

i 

i 

t 

(25). 

6 

4 

1 

i 

i 

(65). 

8 

5 

1 

i 

1 

(140). 

8 

6 

14 

i 

3 
4 

(200). 

10 

6 

2 

i 

1 

(255). 

10 

8 

3 

n 

11 

(435). 

12 

8 

31 

if 

if 

(535). 

12 

10 

54 

2| 

2J 

(815). 

14 

8 

44 

2i 

2i 

(635). 

14 

10 

64 

3t 

3} 

(970). 

14 

12 

9                44 

4! 

(1,355). 

16 

10 

74 

3J 

$J 

(1,130). 

16 

12 

101 

si 

5i 

(1,585). 

16 

14 

14               7 

7 

(2,105). 

18 

12 

12                f> 

6 

(1,810). 

18 

14 

16                8 

8 

(2,415). 

21 


Height. 

Diameter 

Water. 

Acid. 

Cyanide. 

Space  enclosed. 

Feet. 

Feet. 

Fluid  oz. 

Fluid  oz. 

Oz. 

Cubic  Feet. 

18 

16 

20 

10 

10 

(3,085). 

20 

14 

18 

9 

9 

(2,720). 

20 

16 

23 

Hi 

Hi 

(3,485). 

20 

18 

.    29 

14i 

14* 

(4,325). 

22 

18 

32 

16 

16 

(4,835). 

22 

20 

39 

19* 

19i 

(5,865). 

24 

20 

43 

21| 

21i 

(6,500). 

The  cyanide  used  is  between  98  and  100  per  cent,  pure,  and  the 
sulphuric  acid  is  94  per  cent.  pure.  This  grade  of  acid  is  the 
ordinary,  commercial  article;  the  specific  gravity  is  1.84.  Only 
these  grades  of  chemicals  should  be  used  with  this  table.  The 
cyanide  is  weighed  in  avoirdupois  ounces,  and  the  water  and  acid 
measured  in  fluid  ounces. 

The  table  is  based  on  the  assumption  that  proportionate  amounts 
are  required  for  trees  of  different  sizes,  and  that  the  spaco  encom- 
passed by  the  cloth  is  rounded  above.  One  ounce  of  cyanide  is 
taken  as  sufficient  for  300  cubic  feet.  The  approximate  number  of 
cubic  feet  enclosed  is  given  in  the  table  to  show  the  relation  of  one 
tree  to  another.  The  quantity  of  cyanide  allowed  for  the  smallest 
size  of  tree  given  in  the  table  is  slightly  out  of  proportion  to  that 
allowed  for  larger  trees;  the  reason  for  this  is  the  difficulty  of 
working  with  a  quantity  so  small  as  the  proportionate  amount 
without  losing  as  much  in  handling  as  might  vitiate  the  lesults. 
The  table  has  not  yet  been  used  for  trees  over  twenty  feet  in  height. 

For  several  months  a  table  based  on  the  one  published  by  the 
California  State  Board  of  Horticulture  (1893-94  Report,  p.  106)  and 
by  the  Los  Angeles  Horticultural  Commission  was  followed.  The 
quantities  recommended  for  use  in  this  table  are  not  proportionate 
to  the  spaces  enclosed.  This  fact  was  recognised,  but  deeming  that 
the  table  had  been  widely  and  successfully  made  use  of  in  California, 
it  was  thought  perfectly  safe  to  use  one  based  upon  it.  The  results 
were  satisfactory  when  trees  from  8  to  14  feet  were  treated  but  the 
dose  for  smaller  trees  proved  far  too  large,  and  for  larger  trees, 
evidently  too  small. 

An  explanation  of  the  table  was  asked  of  Mr.  Alex.  Craw,  the 
-Entomologist  of  the  California  State  Board  of  Horticulture,  in  a  letter- 
addressed  to  him  in  September,  1896,  but  no  reply  was  condescended. 
Long  puzzling  over  the  table,  however,  has  led  to  the  conviction 
that  the  quantities  are  intended  to  be  proportionate.  It  would 
appear  that  the  proper  amount  for  a  tree  of  medium  size,  presumably 
one  12  feet  in  height,  had  been  ascertained  in  practice,  and  that  the 


22 


amounts  for  smaller  trees  were  taken  as  proportionate  to  the  pro- 
ducts obtained  by  multiplying  the  heights  of  the  trees  by  their 
diameters.  The  amounts  for  larger  trees  were  calculated  in  a 
different  manner,  seemingly  by  increasing  the  amount  by  one  ounce 
(60  per  cent,  cyanide)  for  each  two  feet  additional  in  height  and 
diameter,  or  by  one-half  ounce  when  the  addition  was  two  feet  in  one 
direction  only.  The  difference  of  one  ounce  with  each  two  feet  was 
probably  observed  in  the  computation  of  the  amounts  for  the  smaller 
trees  and  taken  to  be  a  constant  difference  with  this  difference  of 
size.  There  is  no  doubt  about  the  absurdity  of  the  table,  whether 
this  be  the  correct  explanation  of  its  computation  or  not.  The  table 
published  by  Mr.  D.  W.  Coquillett  at  an  earlier  date  is  based  upon 
the  use  of  proportionate  amounts  for  trees  of  different  sizes,  as  is  the 
table  given  here. 


PURPLE  SCALE,  Mytllaspis  citricola,  Pack.  1,  infested  leaf  ;  2,  female  scale  from 
above ;  3,  same  from  beneath ;  4,  male  scale  ;  1  is  natural  size  and  the  others  are 
much  enlarged.  (From  U.S.A.  Dept.  Agr.) 

Known  in  two  orchards  in  the  colony.  This  is  a  very  injurious  scale  in  the 
South  of  Europe  and  in  Florida. 


23 


COST    OF    EQUIPMENT    AND     CHEMICALS. 


Equipment. — The  cloth,  was  furnished  by  Messrs.  J.  W.  Jagger 
&  Co.,  Cape  Town.  The  bulk  of  that  used,  as  already  stated,  was 
"  Burlington  "  eight-ounce  duck,  three-quarters  of  a  yard  in  width. 
This  was  purchased  by  the  piece  of  about  60  yards  at  6|d.  per 
running  yard.  "  Savannah "  eight-ounce  duck  cost  6Jd.  ; 
"Burlington"  ten-ounce,  8Jd. ;  and  "  Savannah "  ten-ounce,  8d. 
"  Greenwoods,"  2  yards  wide,  a  duck  of  about  the  same  quality  as 
the  "  Savannah  "  eight  ounce,  costs  2s.  per  yard ;  and  a  very  heavy 
ten-ounce  duck,  83  yards  wide,  cost  4s.  6d.  in  25  yard  pieces.  Some 
of  all  these  qualities  and  widths  were  used  in  preparing  the  outfit  ; 
"  Burlington "  eight-ounce  would  be  given  the  preference  in 
purchasing  again.  These  American  duck  cloths  resemble  the  cloth 
used  for  wag'gon.  and  cart  hoods. 

The  cutting  and  making  of  each  of  the  smallest  tents  cost  3s.  ;  of 
each  of  Size  II.,  4s.  6d. ;  Size  III.,  7s.  6d. ;  and  Size  IV.,  15s. 
Those  of  the  last  size  were  sewn  by  a  different  party.  The  sheets 
were  sewed  with  two  seams  at  each.  join.  The  sewing  charges 
amounted  to  the  equivalent  of  8d.  per  dozen  yards  of  stitching,  and 
this  charge  included  the  cutting.  The  sewers  were  Jos.  0.  Shirley 
of  Woodstock,  and  James  Lonsdale  of  Wellington. 

The  circles  of  gas-pipe  were  supplied  by  Messrs.  James  Robertson 
&  Co.,  Cape  Town.  The  circles  for  the  smallest  tents  cost  8s.  3d. 
a  piece  ;  those  for  Size  II.  and  Size  III,  12s.  9d. ;  and  those  for  Size 
IV.,  14s.  6d.  The  rings  cost  from  4|d.  to  7d.  per  dozen.  The  lead 
generating  dishes  were  supplied  by  the  same  firm  at  3s.  6d.  each. 

The  uprights  for  raising*  the  sheets  cost  about  20s.  each,  and  the 
ropes  and  pulley  blocks  together  about  23s.  extra.  The  linseed  oil 
and  the  turpentine  used  in  oiling  the  cloth  cost  5s.  and  5s.  6d. 
respectively  per  Imperial  gallon.  The  oiling  was  performed  by  the 
labourers  employed  for  fumigating. 

At  the  prices  paid  for  the  different  articles,  tents  of  eight-ounce 
"  Burlington  "  duck,  made  and  oiled  and  including  the  circle  of  gas- 
pipe,  cost  as  follows  : — 

£    s.    d. 

Size  I.  (  6  breadths  2i  yards  long)  ...  1  2  0 
Size  II.  (  9  breadths  3  yards  long)  ...  1  18  0 
Size  III.  (11  breadths  4  yards  long)  ...  214  0 
Size  IV.  (13  breadths  5  yards  long)  ...  4  0  0 

Size  I.  will  cover  trees  under  5  feet  in  height  and  4  feet  in 
diameter;  Size  II.,  trees  under  7  feet  in  height  and  6  feet  in 
diameter ;  Size  III.,  trees  under  9  feet  in  height  and  7 4  feet  in 
diameter  ;  Size  IV.,  trees  under  12  feet  in  height  ,and  9  feet  in 
diameter.  Somewhat  larger  trees  may  often  be  covered  as  the  tops 
bend  with  the  weight  of  the  cloth,  and  the  side  branches  may  be 
pressed  inward. 


24 

Sheets  made  of  the  same  cloth,  oiled,  and  with  the  sewing- 
charged  at  8d.  per  dozen  yards  of  stitching,  will  cost  as  follows  : — 

£  s.  d. 

32  feet  Across  (14  breadths)        ...                  ...     5  0  0 

38  feet  across  (17  breadths)        ...                  ...     8  0  0 

48  feet  across  (21  breadths)        ...                  ...   15  0  0 

Sheets  of  these  dimensions  will  cover  trees  under  13,  16  and  19 
feet  in  height  respectively.  If  a  sheet  of  larger  dimensions  is 
required  the  addition  of  a  skirt  as  previously  spoken  of  is 
recommended.  This  might  be  of  cheap  drill  or  of  unbleached 
calico,  as  it  will  not  have  to  withstand  a  strain  like  the  body  of  the 
sheet.  A  skirt  three  feet  in  width  would  render  the  largest  sheet 
mentioned  serviceable  for  trees  up  to  21  or  22  feet  in  height.  When 
it  is  desired  to  treat  trees  taller  than  this,  the  cutting  away  of  the 
tops  should  be  considered;  larger  sheets  would  prove  difficult  to 
manipulate  unless  made  of  lighter  cloth. 

Chemicals- — The  cyanide  used  has  all  been  of  98  per  cent, 
purity.  That  employed  during  the  first  six  weeks  was  purchased  of 
Cape  Town  chemists,  the  price  paid  being  5s.  a  pound  plus  jars. 
That  on  order  from  Grermany  then  arrived.  This  cost  Is.  2d.  per 
pound  at  Frankfort  in  a  2  cwt.  zinc-lined  case.  The  carriage  to 
Cape  Town  amounted  to  10s.  A  second  2  cwt  has  since  been  imported 
at  the  same  expense;  but  now  three  2  cwt.  cases  (672  Ibs.)  have 
been  purchased  in  London  from  Messrs.  May  &  Baker,  Battersea, 
at  lOd.  per  pound.  The  total  charges  on  this  lot  to  Cape  Town 
amounted  to  less  than  £29.  If  imported  by  private  parties  there 
would  have  been  a  duty  of  12  per  cent,  and  dock  dues  to  add. 

The  acid  used  has  all  been  ordinary,  commercial  sulphuric  acid 
or  oil  of  vitrol  of  94  per  cent,  purity;  the  specific  gravity  is  1.84.  It 
has  been  purchased  of  Cape  Town  chemists,  50s.  being  paid  for  cases 
containing  four  stone  jars  each  holding  4  2  pounds  of  acid;  lately,  one 
firm  (Wentzel  &  Schleswig)  has  supplied  it  in  cases  containing  2 
stone  jars  holding  62  pounds  for  26s.  a  case.  Single  jars  of  both 
sizes  have  been  purchased  for  14s. 

Expense  Compared  to  Spraying. — Disregarding  the  initial 
equipment  and  labour  required  in  both  cases,  fumigation  is  cheaper 
than  one  thorough  application  of  resin  wash.  At  the  lowest  figures 
known  to  us  for  which  the  ingredients  may  be  purchased  in  Cape 
Town,  resin  wash  (exclusive  of  the  making)  costs  7s.  for  100  imperial 
gallons.  At  least  four  gallons  are  required  to  thoroughly  wet  an 
orange  tree  10  feet  in  height  and  8  feet  in  diameter;  the  four  gallons 
would  cost  at  least  3^d.  Estimating  the  cyanide  to  cost  Is.  4d.  per 
pound  and  the  acid  3d.  per  pound,  the  fumigation  of  a  tree  of  the 
same  size  would  cost  less  than  2Jd.  As  far  as  the  efficacy  of  the 
two  is  concerned,  the  fumigation  is  incomparably  the  superior. 

The  labour  required  for  fumigating  citrus  trees  is  less  under 
favourable  circumstances  than  Jie  labour  necessary  to  spray  the  same 
trees. 


NATURE  OF  HYDROCYANIC  ACID. 


Hydrocyanic  or  Prussic  acid  (H  CN  or  H  Cy)  is  one  of  the  most 
energetic  of  poisons ;  all  animal  life  succumbs  to  it.  It  smells  like 
the  oil  of  bitter  almonds,  and  may  be  obtained  by  distillation  from 
the  kernels  of  bitter  almonds  and  of  many  other  stone-fruits. 
Enough  is  said  to  be  contained  in  one  and  a  half  ounces  of  peack 
kernels  to  kill  a  man.  It  is  extremely  volatile,  and  hence  is  more 
generally  known  in  the  gaseous  than  in  the  liquid  state.  The  gas  is 
lighter  than  air,  and  hence  rapidly  diffuses  when  generated  under  a 
tent.  Water  dissolves  it,  and  for  this  reason  fumigation  is  apt  to  be 
a  failure  when  the  trees  are  wet. 

Animals  fatally  poisoned  with  hydrocyanic  acid  gas  survive  for  a 
longer  or  shorter  period  according  to  the  dose;  death  may  take  place 
as  early  as  the  second  minute  and  as  late  as  the  forty-fifth.  The  chances 
are  favourable  for  recovery  when  the  poison  is  not  fatal  within  an  hour. 
The  nervous  system  is  most  affected ;  death  in  man  is  said  to  be  due 
to  paralysis  of  the  heart-  in  the  most  rapid  cases,  and  to  paralysis  of 
the  respiratory  organs  in  those  which  are  less  quickly  fatal. 
Difficulty  in  breathing,  pains  in  the  head,  giddiness,  nausea,  slowing 
of  the  pulse,  loss  of  muscular  power,  convulsions  with  expulsion  erf 
excretions,  dilation  of  the  pupils  and  protrusion  of  the  eyes,  and, 
finally,  cessation  of  the  pulse  and  breathing  are  given  as  the 
progressive  symptoms.  Chlorine  and  ammonia  are  valuable  as 
antidotes,  but  should  be  administered  only  by  medical  men.  Cold 
water  dashed  on  the  face,  neck  and  over' the  spine  is  valuable  as  a 
remedy,  and  respiration  should  be  kept  up  artificially.  One  or  two 
employes  of  the  Horticultural  Board,  after  working  several 
consecutive  hours  with  the  gas,  have  felt  a  slight  swimming  sensation 
on  nights  when  little  air  was  stirring,  and  the  writer  has  felc 
-considerable  nausea  and  giddiness  as  the  result  of  recklessly 
venturing  into  the  Dock  fumigation  chamber  before  this  had  been 
properly  ventilated  after  the  fumigation  of  fruit.  No  cases  of  fatal 
•or  serious  poisoning  are  known  to  have  anywhere  occurred  to 
operators  of  fumigation  outfits,  but  the  deadly  nature  of  the  gas  has 
often  been  impressed  upon  operators  by  the  untimely  end  of  small 
animals  and  fowls  which  have  been  unintentionally  enclosed  with  the 
tree. 

The  poisonous  action  of  potassium  cyanide  is  nearly  identical  with 
that  of  hydrocyanic  acid  ;  2J  grains  or  about  1/175  of  an  ounce  is 
regarded  as  a  probable  fatal  dose  for  man.  As  this  weight  would 
hardly  suffice  for  a  taste  to  an  inquisitive  person  ignorant  of  the 
nature  of  the  substance,  the  necessity  of  keeping  the  containing 
vessels  plainly  labelled  "  Deadly  Poison  "  and  under  lock  and  key 
when  not  being  used  is  apparent  to  everyone.  There  is  nothing  in  the 
appearance  of  potassium  cyanide  to  indicate  its  nature.  The  form 
used  for  fumigation  purposes  bears  a  superficial  resemblance  to  white 


2(5 

sugar  sweets  (candy),  and  might  easily  be  taken  into  the  mouth  as 
such  by  a  child.  There  is,  however,  always  the  characteristic  odour 
of  hydrocyanic  acid  about  potassium  cyanide. 

Moisture  decomposes  potassium  cyanide,  and  it  is  therefore 
necessary  to  keep  it  in  air-tight  receptacles.  When  moistened  the 
substance  possesses  a  secondary  injurious  action  in  that  it  is  caustic  ; 
the  moisture  of  the  hand  is  often  sufficient  to  cause  it  to  affect  the 
skin  if  handled,  and  likewise  fragments  which  come  in  contact  with 
cloth  or  paper  burn  holes. 

Careful  fumigators  refrain  from  handling  the  substance  with  the 
uncovered  hand,  lest  some  cling  to  the  skin  or  become  lodged  under 
the  nails  and  subsequently  get  introduced  into  the  system  with  food. 
Care  is,  of  course,  always  taken  to  avoid  breathing  the  gas  as  it 
rises  from  the  generating  vessel ;  when  mixed  with  much  air,  as  it 
immediately  becomes  when  the  oloth  is  removed  from  the  tree,  it  is 
not  dangerous. 

Sulphuric  acid  or  oil  of  vitrol  (H.2S04),  the  acid  used  to  liberate 
the  gas,  is  one  of  the  strongest  of  acids ;  it  is  an  odourless,  dense, 
oily -looking  liquid,  almost  as  heavy  again  as  water.  When  pure  it  is 
colourless,  but  the  commercial  article  is  often  brownish,  owing  to  the 
impurities  which  have  fallen  into  it  and  become  charred.  It  is 
intensely  corrosive  and  will  burn  almost  anything  with  which  it 
comes  in  contact.  Many  of  the  metals  are  attacked  and  decomposed. 
When  mixed  with  water  heat  is  evolved.  Painful  burns  are  caused 
by  drops  falling  on  the  skin,  but  as  an  appreciable  period  elapses 
before  it  burns,  the  immediate  rinsiug  of  the  hands  in  water  will 
prevent  injury.  Cloth  is  burnt  even  by  dilute  solutions,  the  acid 
gradually  becoming  stronger  by  the  evaporation  of  the  water.  Care 
must  therefore  be  exercised  not  to  splash  the  cloth  in  adding  the  acid 
to  the  cyanide.  Most  colours  are  changed  to  red  by  the  acid ;  the 
immediate  application  of  ammonia  to  cloth  on  which  it  has  been 
spilled  will  lessen  the  injury. 

The  Cape  Government  Railway  will  convey  sulphuric  acid  on 
certain  trains  only,  and  only  on  the  condition  that  the  jars  containing 
the  acid  are  satisfactorily  packed  in  whiting. 


27 


GENERAL  APPLICABILITY  OF    FUMIGATION  IN 

THE    COLONY. 


Eighteen  months  ago,  the  writer  stated  in  his  annual  report  that 
the  gas  treatment  was  too  expensive  for  general  adoption  in  the 
Colony,  although  in  some  districts  he  believed  it  would  pay  well. 
This  statement  was  based  upon  an  estimate  of  the  cost  of  the  outfit 
and  chemicals  at  the  prices  for  which  the  different  materials  could  be 
purchased  at  retail  in  Cape  Town.  No  draper  would  supply  the  cloth 
at  less  than  Is.  a  yard,  and  no  chemist  would  sell  the  required  grade 
of  cyanide  at  less  than  4s.  6d.  a  pound.  At  these  prices  for  the 
materials,  the  statement  that  fumigation  is  too  costly  for  general 
adoption  is  entirely  unwarranted,  but  it  is  not  in  the  light  of  the 
figures  given  in  the  preceding  paragraphs. 

Kelative  to  the  cyanide,  the  price  has  fallen  over  25  per  cent- 
during  the  last  fifteen  months ;  and  the  writer  is  now  assured  by  a 
Cape  Town  chemist  that  he  will  retail  it  at  about  Is.  9d.  a  pound. 
At  present  little  of  it  is  sold,  and  this  fact  in  part  accounts  for  the 
high  price  which  was  not  lessened  with  the  fall  in  the  wholesale 
price.  Enormous  quantities  are  imported  into  the  Transvaal  and 
used  in  the  extraction  of  gold. 

It  is  now  safe  to  make  the  statement  that,  in  general,  fumigation 
with  hydrocyanic  acid  is  the  cheapest  remedy  for  scale  insects  on 
citrus  trees  in  Cape  Colony.  It  is  not  meant  by  this  that  the  remedy 
is  entirely  applicable  when  a  few  trees  are  concerned,  as  is  generally 
the  case  in  town  and  suburban  gardens.  In  the  majority  of  such 
instances  the  cheapest,  best  and  true  remedy  is  to  uproot  and  burn 
the  trees.  As  long  as  they  remain,  they  are  a  menace  to  the  health 
of  numerous  ornamental  plants  in  their  proximity. 

On  isolated  farms  and  in  sections  where  the  growing  of  citrus 
fruits  is  not  common,  it  will  generally  be  cheapest  and  best  for  each 
grower  to  fumigate  his  own  trees.  An  outfit  for  use  on  a  single 
farm  need  not  be  expensive.  If  the  trees  are  of  about  uniform 
height,  a  single  cover  could  be  made  to  suffice  for  all.  For  the  sake 
of  economy,  the  cloth  should  be  purchased  by  the  piece.  A  single 
piece  would  answer  for  four  Size  I.  tents,  two  Size  II.,  or  one  Size  III, 
and  one  Size  IV.  A  sheet  about  twelve  yards  across  could  be  made 
from  three  pieces  of  cloth,  and  enough  would  remain  for  a  tent  of  Size 
II.  Considerable  saving  could  be  effected  by  having  the  sewing  done 
at  home.  Iron  hoops  from  old  casks  might  be  made  to  serve  the  purpose 
of  the  gas-pipe  circle  for  a  small  tent ;  and  other  means  of  reducing  the 
cost  by  home  makeshifts  will  suggest  themselves  to  the  thrifty  farmer. 

The  trees  might  be  covered  and  the  gas  generated  before  going  in 
to  the  evening  meal,  and  thus  one  or  more  trees,  according  to  the 
number  of  covers,  treated  on  every  favourable  night  without  necessi- 


28 

taking  the  employment  of  extra  labour.  If  for  any  reason  it  is 
inconvenient  to  remove  the  covers  at  the  expiration  of  the  customary 
period,  there  would  be  no  harm  in  leaving  them  on  overnight ;  but  in 
such  cases  one  side  should  be  propped  up  at  the  expiration  of  the  time 
to  allow  the  gas  to  escape  and  care  taken  that  they  are  altogether 
removed  early  in  the  morning. 

To  show  that  there  is  a  demand  and  thus  aid  in  lowering  the 
colonial  price,  quotations  on  the  cyanide  should  be  requested  from 
importers  of  chemical  supplies.  If  over  2s.  6d.  a  pound  in  small  lots  is 
asked,  it  will  probably  be  far  more  profitable  to  import  a  2cwt.  case 
from  London  through  a  commission  merchant.  Several  farmers 
might  combine  to  take  a  case  ;  it  will  not  deteriorate  if  kept  in  air- 
tight tins  or  jars.  A  case  measures  somewhat  less  than  two  feet  each 
Way. 


LONG  SCALE,  Mytilaspis  gloverii,  Pack.  2,  infested  leaf ;  2a,  female  scale  from 
above ;  2c,  same  from  below  ;  26,  male  scale  ;  2  is  natural  size  and  the  others  are  much 
enlarged.  (From  U.S.A.  Dept.  Agr.) 

The  Long  Scale  is  known  in  four  orchards  in  the  colony.  It  has  proved  a  very 
serious  pest  in  Florida. 

Because  of  the  exceedingly  poisonous  nature  of  the  chemicals  used, 
fumigation  by  the  farmer  himself  is  not  recommended  when  the 
farmers  of  a  neighbourhood  or  town,  either  through  their  fruit  grow- 
ers' association  or  otherwise,  can  by  co-operation  prepare  a  large  out- 
fit and  have  their  trees  treated  by  a  trustworthy  party,  preferably 
one  acquainted  with  the  details  of  the  work ;  or  when  a  party  is  at 


29 

hand  who  will  undertake  fumigation  as  a  private  enterprise,  pro- 
viding, of  course,  in  either  case,  that  the  treatment  can  thus  be  econo- 
mically secured.  There  is  nothing  difficult  about  the  work,  nor  is 
previous  experience  or  knowledge  of  chemicals  necessary ;  but  as  in 
almost  any  work  however  simple,  experience  and  knowledge  are 
valuable,  and  especially  so  as  serious  consequences  may  follow  negli- 
gence or  carelessness. 


POINTS    TO    REMEMBER. 


Fumigation  with  hyrdrocyanic  acid  gas  is  by  far  the 
most  successful  remedy  known  for  scale  insects  of  citrus 
trees,  and  it  is  believed  that  such  fumigation  may  be 
economically  employed  on  nearly  all  farms  in  Cape 
Colony  where  citrus  trees  are  grown. 

The  covers  for  the  trees  must  be  free  of  holes  and  be 
of  cloth  which  has  been  made  air-tight. 

The  hydrocyanic  acid  gas  is  generated  by  the  action  of 
sulphuric  acid  on  potassium  cyanide  in  the  presence  of 
water. 

The  trees  are  not  materially  injured  if  the  proper 
amounts  of  the  chemicals  are  used,  and  if  the  opera- 
tions are  carried  on  in  the  absence  of  sun-light. 

The  gas  is  deadly  poisonous  to  man,  and  extreme 
care  should  be  taken  to  avoid  breathing  it  as  it  rises 
from  the  generating  vessel;  mixed  with  air,  it  is  not  so 
poisonous.  Potassium  cyanide  is  as  poisonous  as  the 
gas.  Sulphuric  acid  "  burns "  almost  everything  with 
which  it  is  brought  in  contact. 

The  chemicals  should  always  be  kept  under  lock  and 
key,  and  the  containing  vessels  plainly  labelled  with  the 
name  and  the  warning  "DEADLY  POISON." 

When  feasible  it  is  urged  that  the  farmers  of  a 
neighbourhood  combine  and  engage  a  trustworthy  man 
to  attend  to  the  work ;  but  when  co-operation  is 
impracticable,  it  is  recommended  that  the  farmer  fumi- 
gate his  own  trees. 

The  operations  are  very  simple  and  can  be  safely 
carried  on  by  any  careful  man. 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

JNTOMOLOGY  LIBRARY 

This  book  is  due  on  the  last  date  stamped  below,  or 

on  the  date  to  which  renewed. 
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LD  21-40m-l,'68 
(H7452slO)476 


General  Library 

University  of  California 

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